Currently, high frequency radio frequency (RF) communications are becoming increasingly prevalent. Products touting wireless RF communication links are becoming increasingly popular among consumers. Today, there are an increasing number of new products, in addition to existing products being revamped that are being designed to incorporate wireless RF links.
Due to the explosive consumer demand for products sporting wireless communication links, there is a need for low cost transceivers that are suitable for mass manufacture. In most wireless applications, especially those designed to be mass-produced for the consumer market, it is desirable to reduce both the size and cost of wireless transceivers as much as possible. In the case of time division duplex (TDD) transceivers, manufacturers are constantly striving to reduce the size and cost of the power amplifier and transmit/receive antenna switch portions of the transceiver by integrating these functions onto a single low cost integrated circuit.
Satisfactory performance in such a component can only be achieved by reducing the insertion loss of the antenna switch when in the ‘ON’ state and to enhance the isolation of the switch when it is in the ‘OFF’ state. Presently, in most wireless transceivers designed for the 2.4 GHz ISM frequency band, the transmit/receive antenna switch is typically required to be constructed as an external GaAs RFIC in order to achieve satisfactory performance. Prior art attempts to integrate the transmit/receive antenna switch in a silicon CMOS process have resulted in switches having unacceptably high insertion losses when in the ON state and poor isolation in the OFF state.
In many applications, it is desirable to achieve antenna switch isolation of greater than 20 dB and less than 1 dB of insertion loss. Currently, such performance can only be achieved using external GaAs based RF integrated circuits. Such integrated circuits are based on much more exotic semiconductor processes and are significantly more expensive than conventional silicon based semiconductor processes. The low isolation characteristic of conventional silicon based integrated antenna switches, causes high leakage levels in the switch. In a bi-directional switch this translates to the receive signal leaking into the transmit circuit from the antenna in addition to the leakage of the transmit signal into the receive circuit. The losses due to leakage may be as high as 2 dB on the transmit and receive paths of the transceiver.
There is thus a need for a transmit/receive antenna switch that can be constructed in small size and at low cost using silicon based RF integrated circuit techniques, and is capable of achieving relatively low insertion losses in the ON state and high isolation in the OFF state.